考虑非平衡效应的过冷水滴凝固特性

Freezing characteristics of supercooled water droplet in consideration of non-equilibrium effect

非平衡凝固是过冷条件下水滴凝固过程的重要现象。本文针对飞机结冰过程过冷水滴的非平衡凝固效应,发展了改进的凝固特性预测模型及数值计算方法,并自行搭建了实验系统,开展了所建过冷水滴凝固模型与数值预测方法的实验验证。研究表明,所发展的改进模型可有效表征水滴过冷阶段的非平衡凝固效应,因而对冷水滴凝固速率的预测有较好的改进;当过冷度为0℃时,过冷模型退化为传统模型。基于所建方法,开展了过冷度及冷却条件对水滴凝固特性的影响分析,获得了不同条件下水滴凝固过程的温度分布及相界面变化特征。研究表明,过冷度越大或水滴尺度越小,凝固速率相对越高;在考虑非平衡凝固效应的条件下,过冷水滴凝固速率要高于不考虑非平衡凝固效应的工况。相关研究可为结冰热力学模型的改进,以及结冰特性的精细化预测提供参考。

Non-equilibrium effect is an important phenomenon in freezing of supercooled water droplet in aircraft icing process.Based on the enthalpy-porosity model,a numerical prediction method for freezing of supercooled water droplet is developed.The experimental system for droplet freezing is built up and several experiments are performed to validate the numerical method proposed.The results indicate that the developed model is valid and can be used to predict the freezing characteristics of supercooled water droplet.Based on the improved freezing model,the influence of the degree of supercooled and cooling conditions on the characteristics of supercooled droplet are analyzed.When the degree of supercooled is decreased to zero,the developed model degenerates to the traditional model.The greater or smaller the degree of supercooled or smaller the droplets is,the relatively higher freezing rate is.In consideration of the effect of non-equilibrium conditions,the freezing and moving rate of interface is higher than the traditional model.Related research can provide important reference for improving icing thermodynamic model and refining the prediction method for icing accretion.